Cast tires comprised of a body without reinforcing cords which are made by a liquid casting, or injection molding, process using a viscoelastic material are known. Such tires with cast viscoelastic material treads or with conventional rubber treads are known. It is now believed that cast tires require a conventional rubber tread to have adequate traction and tread wear.
The dimensional stability of a cast body tire has long been known to be a major drawback. This feature manifests itself by the growth of the tire; that is, an increase in the overall diameter of the tire and/or the section width of the tire and a decrease in the tread radius of the tire upon inflation and use. Several constructions have been successful to control this growth. The most successful has been the incorporation of a girdle member in the crown area of the tire below the road-engaging tread surface.
This girdle member is comprised of parallel reinforcing cords that form a layer or a series of layers or plies. The reinforcing cords within each ply are parallel to one another. Where two or more plies are used, the cords from ply to ply may have various angulations or their angulation may be identical.
A major drawback to the use of a girdle member in the cast tire has been the lack of an accurate and reproducible method for locating the girdle member at the desired location in the tire. This is due to the fact that the girdle member must be located in the mold at a position that is surrounded by the flowable material during the casting operation.
The location of the girdle member in the cast tire is critical and must be closely controlled. If the girdle member is not properly located, proper dynamic balance and the dimensional stability of the tire may not be attained. The tire would therefore be unsatisfactory and would not give the performance characteristics that are required.
One attempt to locate such a member is set out in German Offenlegungsschrift No. 2,619,942. This disclosure provides a ply of inextensible, parallel wires with retaining brackets that have pins which extend radially outward from the parallel cords. The pins are set into a precured and prepositioned tread in the mold. The retaining brackets for the pins also are in contact with and supported by the mold at the lateral ends of the brackets. This technique has the drawbacks that the location of a precured tread in the mold and the dimensions of the precured tread itself are not accurate enough to ensure the accurate and reproducible location of the girdle member.
Prior methods of belt placement have not had the important capability of maintaining a selected tension on the cords in the belt member. The tension on the cords predetermines the forces in the cords. When the designed cord tensions are maintained a better performance and more uniform tire results. The method of this invention enables an accurate control of the tension on the girdle member cords all the way through the manufacturing process and into the final product. The method of this invention also enables uniform cord tension even when the girdle member has a designed radius.
The applicant has devised a new method of manufacturing a cast tire containing a girdle member that enables the accurate, reproducible placement of the girdle member at the designed location in the cast tire. The method also provides for the maintenance of a predetermined tension on the girdle member cord throughout the process and the capability of providing the girdle member with a radius.
It is an object of this invention to provide a method of manufacturing a cast tire wherein the dimensional stability is obtained by a girdle member located in the crown area of the tire. The method of this invention enables the accurate, reproducible location of this girdle member at the desired, predetermined optimum place in the tire, the maintenance of a preselected tension on the girdle member cords throughout the manufacturing process, and the presence of a radius in the girdle member, if desired.